The present invention relates in general to a controller for an air conditioner and, more particularly, to the controller for preventing the simultaneous starting of a plurality of air conditioner compressors, the air conditioners being driven by the same AC power source, when the AC power is restored after a power failure.
A conventional controller for an air conditioner having a refrigeration cycle is disclosed in Japanese Utility Model Publication No. 59-30818/1984. The controller disclosed therein has an operation switch for starting and stopping the air conditioner, a thermostat, and a compressor, all connected in series with an AC power source. With this series connection, when the operation switch in the operating positions (i.e., positions of high power cooling, medium power cooling, light power cooling) and the thermostat is turned on, the compressor is energized and started. The timer is always turned on.
When a plurality of conventional air conditioners are driven by the same AC power source, as in a case where several hundred rooms in a hotel are each provided with an air conditioner, a power failure caused by trouble occurring outside the hotel facilities will stop all of the air conditioners until the power is restored. When the power is restored, the compressors are immediately and automatically restarted.
The arrangement of the conventional air conditioners described above, however, has disadvantages. Suppose a power failure occurs when several hundreds of air conditioners are in operation. When the power is restored, all of the air conditioners simultaneously start, that is, several hundred compressors are started at once, causing a great amount of starting electric current to flow in the power supply system, which in turn causes a voltage drop in the AC power. One solution to this problem is an increase of the capacity of the AC power source but this requires substantially larger power facilities as compared to that required for the normal operation.
Japanese Utility Model Publication No. 62-43391/1987 discloses a controller which has microcomputer with a reset circuit for resetting microcomputer when electric power is supplied. The reset circuit has a voltage detector which outputs a reset signal when a DC voltage from a constant voltage circuit becomes higher than a predetermined voltage, and a timer circuit for delaying, for a predetermined length of time, the output of the voltage detection and then supplies it to the reset terminal of the microcomputer. The reset circuit resets the microcomputer after a predetermined time period from the time when the DC voltage becomes higher than the predetermined voltage. This configuration ensures the reset of the microcomputer only after the voltage to the microcomputer is completely established and, therefore, the microcomputer is reliably started in accordance with an initialization program therefor.
In the controller for the air conditioners with microcomputers as described above, the delay times of the reset signals are distributed over a range to some extent among different microcomputers because of the characteristic variations of electronic parts in each of the microcomputers, which sometimes permits, by chance, reduction of the starting current at the time of power restoration. However, the range of delay time distribution is limited, so that the starting current cannot be reduced sufficiently, with the result that large power facilities are still required.